Piezoelectric element, piezoelectric actuator, ink jet recording head, ink jet printer, surface acoustic wave element, frequency filter, oscillator, electronic circuit, thin film piezoelectric resonator, and electronic apparatus

ABSTRACT

A piezoelectric element is provided that is equipped with a seed layer formed on a base substrate and a piezoelectric film formed on the seed layer. The seed layer is formed of a perovskite type piezoelectric material preferentially oriented to pseudo cubic (100). The piezoelectric film is formed of a relaxor material that has a perovskite type rhombohedral structure, and is preferentially oriented to pseudo cubic (100).

RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No.2004-017108 filed Jan. 26, 2004 which is hereby expressly incorporatedby reference herein in its entirety.

BACKGROUND

1. Technical Field

The present invention relates to piezoelectric elements, piezoelectricactuators, ink jet recording heads, ink jet printers, surface acousticwave elements, frequency filters, oscillators, electronic circuits, thinfilm piezoelectric resonators, and electronic apparatuses, which havepiezoelectric films.

2. Related Art

An inkjet printer is known as a printer that enables a high resolutionpicture quality and a high-speed printing. An inkjet printer is equippedwith an ink jet recording head that has a cavity whose volume changes.Ink droplets are discharged from its nozzle while scanning the head,whereby printing is performed. As a head actuator in the ink jetrecording head for such an inkjet printer, a piezoelectric element thatuses a piezoelectric film, which is represented by PZT (Pb (Zr, Ti) O₃),is conventionally used (see, for example, Japanese Laid-open PatentApplication 2001-223404).

Moreover, because the characteristics of surface acoustic wave elements,frequency filters, oscillators, and electronic circuits are desired tobe improved, excellent products with novel piezoelectric materials areexpected to be supplied.

It is noted that higher picture quality and faster printing speed are indemand in inkjet printers. To meet such a demand, the technology to makenozzles in an ink jet recording head to have a higher density becomesindispensable. In order to achieve this, piezoelectric elements (headactuators) that are laminated over cavities, and in particular, thecharacteristics of piezoelectric films, in other words, theirpiezoelectric constant need to be improved.

The present invention has been made in view of the problems describedabove, and its object is to provide piezoelectric elements equipped withpiezoelectric films having a high piezoelectric constant, and to provide

-   -   piezoelectric actuators, ink jet recording heads, ink jet        printers, surface acoustic wave elements, frequency filters,        oscillators, electronic circuits, thin film piezoelectric        resonators, and electronic apparatuses, which use the        piezoelectric films.

SUMMARY

To achieve the object described above, a piezoelectric element inaccordance with the present invention is equipped with a seed layerformed on a base substrate and a piezoelectric film formed on the seedlayer, and is characterized in that

-   -   the seed layer is formed of a perovskite type piezoelectric        material preferentially oriented to pseudo cubic (100), and    -   the piezoelectric film is formed of a relaxor material of a        perovskite type that is preferentially oriented to pseudo cubic        (100).

Or, a piezoelectric element is equipped with a seed layer formed on abase substrate and a piezoelectric film formed on the seed layer, and ischaracterized in that

-   -   the seed layer is formed of a perovskite type piezoelectric        material preferentially oriented to pseudo cubic (100), and    -   the piezoelectric film is formed of a relaxor material of a        perovskite type having a rhombohedral structure, that is        preferentially oriented to pseudo cubic (100).

The seed layer may preferably be formed of Pb(ZrTi)O₃.

Or, the seed layer may preferably be composed of a plurality of layers,wherein a composition of each layer among the plurality of layers may bedifferent from one another.

Or, the seed layer may preferably be composed of a plurality of layers,wherein a lowermost layer among the plurality of layers may be a PbTiO₃,and a layer formed over the lowermost layer may be a Pb(ZrTi)O₃.

Also, the relaxor material may preferably be formed of at least one typeamong materials shown by the following formulae:(1−x)Pb(Sc_(1/2)Nb_(1/2))O₃-xPbTiO₃

-   -   (where, x is 0.10<x<0.42)        (1−x)Pb(In_(1/2)Nb_(1/2))O₃-xPbTiO₃    -   (where, x is 0.10<x<0.37)        (1−x)Pb(Ga_(1/2)Nb_(1/2))O₃-xPbTiO₃    -   (where, x is 0.10<x<0.50)        (1−x)Pb(Sc_(1/2)Ta_(1/2))O₃-xPbTiO₃    -   (where, x is 0.10<x<0.45)        (1−x)Pb(Mg_(1/3)Nb_(2/3))O₃-xPbTiO₃    -   (where, x is 0.10<x<0.35)        (1−x)Pb(Fe_(1/2)Nb_(1/2))O₃-xPbTiO₃    -   (where, x is 0.01<x<0.10)        (1−x)Pb(Zn_(1/3)Nb_(2/3))O₃-xPbTiO₃    -   (where, x is 0.01<x<0.09.)        (1−x)Pb(Ni_(1/3)Nb_(2/3))O₃-xPbTiO₃    -   (where, x is 0.10<x<0.38)        (1−x)Pb(Co_(1/2)W_(1/2))O₃-xPbTiO₃    -   (where, x is 0.10<x<0.42).

According to the piezoelectric element, because the piezoelectric filmformed of a relaxor material is formed on the seed layer that ispreferentially oriented to (100), the piezoelectric film also becomespreferentially oriented to pseudo cubic (100), such that it has a highpiezoelectric constant, and exhibits a larger deformation to an appliedvoltage.

Also, by using a relaxor material shown by each of the formulaedescribed above as a piezoelectric film, its piezoelectric constantbecomes sufficiently high, and the piezoelectric film exhibits a betterdeformation.

It is noted that the case of “being preferentially oriented” includes acase where most of the crystals (for example, 90% or more) are in adesired (100) orientation, and the remaining crystals are in anotherorientation (for example, (111) orientation), and also includes a casewhere 100% of the crystals are in a desired (111) orientation.

Moreover, in an ink jet recording head equipped with a cavity having avolume that changes, the piezoelectric element described above maychange the volume of the cavity by a deformation of the piezoelectricfilm.

By providing the piezoelectric element (as a head actuator) in the inkjet recording head, ink can be excellently discharged by its excellentpiezoelectric characteristics.

A piezoelectric actuator in accordance with the present invention ischaracterized in comprising the piezoelectric element described above.The piezoelectric actuator excellently functions due to thepiezoelectric characteristics described above.

An ink jet recording head in accordance with the present inventionpertains to an ink jet recording head having a cavity having a volumethat changes, and is characterized in comprising the piezoelectricelement described above as a piezoelectric element that changes thevolume of the cavity by a deformation of a piezoelectric film.

By the ink jet recording head, ink can be excellently discharged by theexcellent piezoelectric characteristics described above. Also, inparticular, because the piezoelectric film has a high piezoelectricconstant and exhibits a greater deformation to an applied voltage, thecavity area (volume) required to discharge a predetermined amount of inkcan be smaller compared to the conventional system, and thereforenozzles can be arranged in a higher density.

An ink jet printer in accordance with the present invention ischaracterized in comprising the ink jet recording head described above.

Because the ink jet printer is equipped with an ink jet recording headthat has a high performance and whose nozzles can be arranged in a highdensity, a high-speed printing becomes possible.

A surface acoustic wave element in accordance with the present inventionis characterized in comprising the piezoelectric element recited aboveformed on a substrate.

According to the surface acoustic wave element, the piezoelectric filmof the piezoelectric element has excellent piezoelectriccharacteristics, such that the surface acoustic wave element itself hasa high performance.

A frequency filter in accordance with the present invention ischaracterized in comprising: a first electrode that is formed on thepiezoelectric film of the surface acoustic wave element described above;and a second electrode that is formed on the piezoelectric film,resonates at a specified frequency or a specified band frequency insurface acoustic waves generated in the piezoelectric film by anelectrical signal applied to the first electrode, and converts the sameto an electrical signal.

According to the frequency filter, its piezoelectric film has excellentpiezoelectric characteristics and therefore the piezoelectric film has ahigh electromechanical coupling factor, such that its specific bandwidthis wide and excellent.

An oscillator in accordance with the present invention is characterizedin comprising: an oscillation circuit including an electrical signalapplication electrode that is formed on the piezoelectric film of thesurface acoustic wave element described above, and generates surfaceacoustic waves in the piezoelectric film by an electrical signalapplied; and a resonation electrode that is formed on the piezoelectricfilm, and resonates at a specified frequency or a specified bandfrequency in the surface acoustic waves generated by the electricalsignal application electrode, and transistors.

According to the oscillator, because the piezoelectric film hasexcellent piezoelectric characteristics, and therefore the piezoelectricfilm has a high electromechanical coupling factor, such that extensioncoils can be omitted, and thus the circuit structure becomes simple.Also, because it is equipped with the oscillation circuit formed fromtransistors and the like, it can be miniaturized through integration ofthe transistors.

An electronic circuit in accordance with the present invention isequipped with the oscillator described above, and an electrical signalsupplying element that applies the electrical signal to the electricalsignal application electrode provided in the oscillator, and ischaracterized in comprising the functions to select a specifiedfrequency component from frequency components of the electrical signalor convert the frequency components to a specified frequency, or to givea predetermined modulation to the electrical signal to conduct apredetermined demodulation or conduct a predetermined detection.

Accordingly, because the piezoelectric film composing the surfaceacoustic wave element provided in the oscillator has excellentpiezoelectric characteristics, and therefore the piezoelectric film hasa high electromechanical coupling factor, the electronic circuit can beintegrated with an oscillation circuit, such that it becomes smaller insize and higher in performance.

A thin film piezoelectric resonator in accordance with the presentinvention is characterized in comprising a resonator that is formed fromthe piezoelectric element described above on a base substrate.

Because the piezoelectric film of the resonator has a highelectromechanical coupling factor, the thin film piezoelectric resonatorcan be used in a high-frequency area, such as, for example, a GHz band.

It is noted that, with such a thin film piezoelectric resonator, a viahole may be formed on an opposite side of the side of the base substratewhere the resonator described above is formed, whereby a diaphragm typethin film piezoelectric resonator can be formed.

Also, by forming an air gap between the base substrate and theresonator, an air gap type thin film piezoelectric resonator can beformed.

An electronic apparatus in accordance with the present invention ischaracterized in comprising at least one of the above-describedfrequency filter, oscillator, electronic circuit, and thin filmpiezoelectric resonator.

Because the piezoelectric film has excellent piezoelectriccharacteristics, and therefore the piezoelectric film has a highelectromechanical coupling factor, the electronic apparatus becomesminiaturized and has a higher performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a piezoelectric element inaccordance with an embodiment of the present invention.

FIGS. 2( a) and (b) are graphs for describing relaxor materials

FIGS. 3( a)-(e) are views showing steps of manufacturing a piezoelectricelement.

FIG. 4 is a view schematically showing a structure of an ink jetrecording head.

FIG. 5 is an exploded perspective view of the ink jet recording head.

FIGS. 6( a) and (b) are views for describing operations of the head.

FIG. 7 is a view schematically showing a structure of an ink jetrecording in accordance with the present invention.

FIG. 8 is a side cross-sectional view of a surface acoustic wave elementin accordance with the present invention.

FIG. 9 is a perspective view of a frequency filter in accordance withthe present invention.

FIG. 10 is a perspective view of an oscillator in accordance with thepresent invention.

FIG. 11 is a view schematically showing an example in which theoscillator is applied as a VCSO.

FIG. 12 is a view schematically showing an example in which theoscillator is applied as a VCSO.

FIG. 13 is a block diagram showing the basic structure of a PLL circuit.

FIG. 14 is a block diagram showing the structure of an electroniccircuit in accordance with the present invention.

FIG. 15 is a perspective view showing a cellular telephone as one typeof electronic device according to an embodiment of the presentinvention.

FIG. 16 is a side cross-sectional view showing a thin film piezoelectricresonator in accordance with the present invention.

FIG. 17 is a side cross-sectional view showing a thin film piezoelectricresonator in accordance with the present invention.

DETAILED DESCRIPTION

The present invention is described in detail below.

Piezoelectric Element

First, a piezoelectric element in accordance with the present inventionthat is obtained by a method for manufacturing a ferroelectric thin filmin accordance with the present invention is described.

FIG. 1 is a view showing an embodiment in which a piezoelectric elementof the present invention is applied to a piezoelectric element thatbecomes to be a head actuator, in particular, for an ink jet recordinghead, wherein reference numeral 1 in FIG. 1 denotes a piezoelectricelement.

Also, the piezoelectric element can be used as a piezoelectric actuatorother than as the head actuator for an ink jet recording head.

The piezoelectric element 1 is formed on a substrate 2 formed of silicon(Si), and has a structure having an elastic film 3 formed on thesubstrate 2, a lower electrode 4 formed on the elastic film 3, a seedlayer 5 formed on the lower electrode 4, a piezoelectric film 6 formedon the seed layer 5, and an upper electrode 7 formed on thepiezoelectric film 6. It is noted here that, in the present invention, aportion from the substrate 2 up to the lower electrode 4 is referred toas a base substrate.

It is noted that, as the substrate 2, a single-crystal silicon substratewith a (100) orientation, a single-crystal silicon substrate with a(111) orientation, or a Si substrate with a (110) orientation can beused. Also, a substrate having an amorphous oxide silicon film such as athermal oxidation film, a natural oxidation film or the like formed onits surface can be used.

The elastic film 3 formed on the substrate 2 is a film that functions asan elastic plate in the piezoelectric element that becomes a headactuator for an inkjet recording head, is formed of SiO₂, ZrO₂ or thelike, and is thickly formed to a thickness of, for example, about 1 μm.It is desirable to form the elastic film 3 with a material that can takea sufficient selection ratio with Si such as SiO₂ and ZrO₂ describedabove, such that the elastic film 3 functions as an etching stopperlayer when a cavity is formed here by etching the substrate 2 asdescribed below. It is noted that, when multiple piezoelectric elementsare formed on the substrate 2 that becomes an ink chamber substrate inthe inkjet recording head to be described below, the elastic film 3 canbe formed as a common elastic plate for them.

The lower electrode 4 becomes to be one of electrodes for applying avoltage to the piezoelectric film 6, and is formed, for example, in thesame size as that of the piezoelectric film 6 as indicated in FIG. 1, inother words, in the same configuration as that of the upper electrode 7.It is noted that, when multiple piezoelectric elements are formed on thesubstrate 2 that becomes an ink chamber substrate in the inkjetrecording head to be described below, the lower electrode 4 can beformed in the same size as the elastic film 3 that defines a commonelastic plate, so as to function as a common electrode for them.Furthermore, the lower electrode 4 is formed from Pt (platinum), Ir(iridium), IrO_(x) (iridium oxide), Ti (titanium) or the like, to athickness of about 100 nm-200 nm.

The seed layer 5 is formed of a piezoelectric material of a perovskitetype and is preferentially oriented to pseudo cubic (100). Morespecifically, as a lead system material, lead titanate (PbTiO₃), PZT (Pb(Zr_(x)Ti_(y))O₃; x+y=1), (Pb(Zr_(x)Ti_(y)M_(z))O₃; M=Nb, Ta, V,x+y+z=1), and other lead titanate derivatives can be enumerated. As anon-lead system material, BaTiO₃, (Ba_(a)A_(b)) (M_(x)Ti_(y))O₃ (A=Sr,Ca, a+b=1, M=Zr, Hf, x+y=1), and the like are enumerated. Thesepiezoelectric materials can be formed into a film on the lower electrode4 by a liquid phase method or a vapor phase method, and can bepreferentially oriented to pseudo cubic (100) by appropriatelycontrolling, in particular, the temperature condition (heatingcondition) in this instance. It is noted here that the case of “beingpreferentially oriented” includes a case in which most of the crystalsare oriented to a desired (100) orientation and the rest is oriented toother orientations, as described above. When most of the crystals areoriented to a desired (100) orientation, the piezoelectric film 6, whenthe piezoelectric film 6 is formed thereon as described below, succeedsthe crystal structure of the seed layer 5, and has the same crystalstructure, in other words, is preferentially oriented to (100).

Because the seed layer 5 is formed of a piezoelectric material, it doesnot function as the lower electrode 4 but rather slightly demonstrates afunction as the piezoelectric film 6 as described below, and itinfluences the piezoelectric characteristics (helps the piezoelectriccharacteristics) of the piezoelectric film 6. Therefore, if the filmthickness of the seed layer 5 becomes too large, the influence of thepiezoelectric film 6 on the piezoelectric characteristics becomes toolarge. Therefore, the thickness of the seed layer may preferably be 100nm or less, and more preferably, 50 nm or less, such that the influencedoes not grow more than necessary. Also, a typical film thickness of thepiezoelectric film 6 is 300 nm to 3.0 μm. The upper limit of thethickness is not limited, as long as it is within the range to sustainthe density and the crystal orientation as a thin film, and may beallowed up to 10 μm.

The piezoelectric film 6 is formed from a relaxor material that has aperovskite type rhombohedral structure, and preferentially oriented topseudo cubic (100), and is formed to a thickness of about 500 nm-1000nm. As the relaxor material, for example, materials shown by thefollowing formulae can be enumerated. One type or multiple typesselected from among these materials is formed into a film by a liquidphase method or a vapor phase method, whereby the piezoelectric film 6can be obtained.(1−x)Pb(Sc_(1/2)Nb_(1/2))O₃-xPbTiO₃

-   -   (where, x is 0.10<x<0.42, more preferably, 0.20<x<0.42)        (1−x)Pb(In_(1/2)Nb_(1/2))O₃-xPbTiO₃    -   (where, x is 0.10<x<0.37, more preferably, 0.20<x<0.37)        (1−x)Pb(Ga_(1/2)Nb_(1/2))O₃-xPbTiO₃    -   (where, x is 0.10<x<0.50, more preferably, 0.30<x<0.50)        (1−x)Pb(Sc_(1/2)Ta_(1/2))O₃-xPbTiO₃    -   (where, x is 0.10<x<0.45, more preferably, 0.20<x<0.45)        (1−x)Pb(Mg_(1/3)Nb_(2/3))O₃-xPbTiO₃    -   (where, x is 0.10<x<0.35, more preferably, 0.20<x<0.35)        (1−x)Pb(Fe_(1/2)Nb_(1/2))O₃-xPbTiO₃    -   (where, x is 0.01<x<0.10, more preferably, 0.03<x<0.10)        (1−x)Pb(Zn_(1/3)Nb_(2/3))O₃-xPbTiO₃    -   (where, x is 0.01<x<0.09, more preferably, 0.03<x<0.09)        (1−x)Pb(Ni_(1/3)Nb_(2/3))O₃-xPbTiO₃    -   (where, x is 0.10<x<0.38, more preferably, 0.20<x<0.38)        (1−x)Pb(Co_(1/2)W_(1/2))O₃-xPbTiO₃    -   (where, x is 0.10<x<0.42, more preferably, 0.20<x<0.42).

It is noted here that a relaxor material is a material whosetemperature-dependence of dielectric constant exhibits a broad (wide)peak as indicated in FIG. 2( a), and in which the temperature at whichits dielectric constant becomes maximum shifts according to frequenciesmeasured. Also, its temperature dependence of piezoelectric constantconcurrently exhibits a broad (wide) peak. In contrast, in apiezoelectric material such as PZT, which is a non-relaxor material, itstemperature dependence of dielectric constant and piezoelectric constantexhibit a very sharp peak as indicated in FIG. 2( b). Accordingly, byusing a relaxor material for the piezoelectric film 6, the piezoelectricelement 1 obtained exhibits excellent piezoelectric characteristics in abroad temperature range, whereby its reliability becomes high and itscharacteristics becomes stable.

Moreover, the piezoelectric film 6 has a rhombohedral structure of aperovskite type, and is preferentially oriented to pseudo cubic (100),which is coordinated in an engineered domain, and therefore has a highpiezoelectric constant (d₃₁). It is noted here that the case of “beingpreferentially oriented” includes a case in which most of the crystalsare oriented to a desired pseudo cubic (100) orientation, but the restis oriented to other orientations, as described above. In other words,because the piezoelectric film 6 is formed on the seed layer 5 that ispreferentially oriented, and thus has a crystal structure that succeedsthe crystal structure of the seed layer 5, the piezoelectric film 6 ispreferentially oriented to (100), like the seed layer 5.

In the material that forms the piezoelectric film 6 (relaxor material),as for the aforementioned range of x indicating the composition ratioamong the materials on the PbTiO₃ (PT) side, in particular, its upperlimit is assumed to be a value indicating a composition ratio of thePbTiO₃ (PT) side at its morphotropic phase boundary (MPB), in otherwords, at which a phase change takes place between rhombohedralstructure and tetragonal structure. The value x is assumed to range froma value smaller than the composition ratio at the phase change to avalue at which the phase becomes the rhombohedral structure. It is notedhere that the d constant (d₃₁), that is a piezoelectric constant,becomes to be the maximum value around the morphotropic phase boundary(MPB). Accordingly, as the lower limit value of the value x, a valueclose to the value x at the MPB is selected. Therefore, althoughrelatively small values are permissible in the range of x for achievingthe present invention, values in the preferred range, in other words,values that are close to the value x at the MPB, may be selected inorder to obtain a higher d constant (d₃₁), i.e., higher piezoelectricconstant.

Conventionally, a complex technique is required to form thepiezoelectric layer 6, which is formed of a relaxor material that has aperovskite type rhombohedral structure and is preferentially oriented topseudo cubic (100). For example, a buffer layer is formed by using alaser ablation method, together with a complex technique such as an ionbeam assisted method, a groundwork is formed thereon by forming a lowerelectrode of a perovskite type, and then a piezoelectric film is formedover the groundwork. The reason to adopt such a technique is that themanufacturing margin to form a dense thin film of a relaxor material ona conventional electrode material such as Pt and Ir is small, while adense thin film can be relatively easily obtained on an electrode of aperovskite type material such as SrRuO₃, and to control the orientationof the SrRuO₃ electrode, the laser ablation method and the ion beamassisted method are needed. However, there is a difficulty in that sucha technique involves complicated processes, such that the cost is raisedand piezoelectric characteristics of the piezoelectric film obtained arenot stable enough. PZT and BaTiO₃ can form a dense thin film on a Pt orIr electrode, with its orientation being controlled to some degree. Inaddition, a relaxor material such as PMN•PT can be readily laminated asa dense thin film on a dense PZT and BaTiO₃ layer that is once formed.Therefore, in the present invention, the seed layer 5 that is formed ofPZT or the like is formed beforehand as described above, and thepiezoelectric film 6 that is formed of a relaxor material is formedthereon, whereby the piezoelectric film 6 with excellent piezoelectriccharacteristics can be readily formed even by a liquid phase method thatinvolves simpler processes compared to a vapor phase method, asdescribed below.

The upper electrode 7 becomes the other electrode to apply a voltage tothe piezoelectric film 6, and is formed of, for example, Pt (platinum),Ir (iridium), IrO_(x) (iridium oxide), Ti (titanium), SrRuO₃ or thelike, like the lower electrode 4, which is formed to a thickness ofabout 100 nm.

It is noted that the use of a perovskite electrode such as a SrRuO₃electrode as the lower electrode 4 does not deviates from the subjectmatter of the present invention. If a seed layer such as PZT is placedbetween the lower electrode 4 formed of SrRuO₃ and the piezoelectricfilm 6 formed of a relaxor material, the pseudo cubic (100) orientationof the piezoelectric film 6 can be more readily controlled in themanufacturing process.

Next, a method for manufacturing the piezoelectric element 1 having sucha structure is described.

First, as a substrate 2, a single-crystal Si substrate with a (110) or(100) orientation, a single-crystal Si substrate with a (111)orientation, or a Si substrate with a (100) or (110) orientation with anamorphous silicon oxide film that is a natural oxidation film formedthereon is prepared.

Next, an elastic film 3 is formed on the substrate 2 as shown in FIG. 3(a). For the elastic film 3, a vapor phase method such as a CVD method, asputter method, or the like is properly decided and adopted according tothe material to be formed.

Next, a lower electrode 4 that is formed of Pt, for example, is formedon the elastic film 3, as shown in FIG. 3( b). Because this Ptrelatively readily becomes preferentially oriented to (111), it can bereadily oriented and grown on the elastic film 3 by using, for example,a relatively simple method such as a sputter method or the like.

Next, a seed layer 5 is formed on the lower electrode 4, as shown inFIG. 3( c). More specifically, a precursor solution of the perovskitetype piezoelectric material described above is disposed on the lowerelectrode 4 by a well-known coating method, such as, a spin coat method,a droplet discharge method, or the like, and then a heat-treatment suchas sintering or the like is conducted to thereby obtain the seed layer5. Concretely, a series of steps of a precursor solution coating step, adry thermal treatment step, and a cleaning thermal treatment step isrepeated a desired number of times depending on the desired filmthickness, and then crystallization annealing is conducted to form theseed layer 5. Conditions in each of the steps are for example asfollows.

In the precursor solution coating step, if the precursor solution iscoated by a spin coat method, first, the precursor solution is drippedon the lower electrode 4. In order to spread the dripped solution overthe entire surface of the substrate, spinning is conducted. The rotationspeed of the spinning may be, for example, about 500 rpm in an initialstage, and can be increased in succession to about 2000 rpm such thatcoating irregularities do not occur, and then the coating is completed.

In the dry thermal treatment step, a heat treatment (dry treatment) isperformed in the atmosphere, using a hot plate or the like, attemperatures that are about 10° C. higher than the boiling point of thesolution used in the precursor solution, for example.

In the cleaning thermal treatment step, a heat treatment is performed inthe atmosphere, using a hot plate, at about 350° C. to dissolve andremove ligands of the organic metals used in the precursor solution.

In crystallization annealing, in other words, in the sintering step forcrystallization, a thermal treatment is performed in an oxygenatmosphere, at about 600° C., for example, by using the rapid thermalanneal (RTA) method or the like.

By forming the seed layer 5 on the lower electrode 4 formed of Pt with a(111) orientation in the manner described above, a perovskite structuretype piezoelectric is formed in a state preferentially oriented to(100).

Next, as shown in FIG. 3( d), a piezoelectric film 6 is formed on theseed layer 5. More specifically, a precursor solution of the relaxormaterial described above is disposed on the seed layer 5 by a well-knowncoating method, such as, a spin coat method, a droplet discharge method,or the like, and then a heat-treatment such as sintering or the like isconducted to thereby obtain the piezoelectric film 6. Concretely, in amanner similar to the case of forming the seed layer 5, a series ofsteps of a precursor solution coating step, a solution removal step, adry thermal treatment step, and a cleaning thermal treatment step isrepeated a desired number of times depending on the desired filmthickness, and then crystallization annealing is conducted to form thepiezoelectric film 6. Conditions in each of the steps are generally thesame as those in forming the seed layer 5.

The piezoelectric film 6 thus formed, as being formed on the seed layer5 that is preferentially oriented to (100), succeeds the crystalstructure of the seed layer 5, in other words, the orientation thereof,and would have the same crystal structure, in other words,preferentially oriented to psuedo cubic (100).

The precursor solution that is the forming material of the seed layer 5or the piezoelectric film 6 is formed as follows.

Organic metals that include constituent metals of the piezoelectricmaterial or the relaxor material, respectively, that becomes the seedlayer 5 or the piezoelectric film 6, in other words, the organic metalssuch as metal alkoxide and organic acid salt are mixed such that each ofthe metals becomes a desired molar ratio, and they are dissolved ordispersed by using an organic solvent such as alcohol. A variety ofadditives, such as, stabilization agent may be added to this precursorsolution if necessary. In addition, when hydrolysis or polycondensationis to be caused in the solution, acid or base can be added to thesolution as a catalyst with an appropriate amount of water.

In the present embodiment, the seed layer 5 as well as the piezoelectricfilm 6 is formed by a liquid phase method, but the seed layer 5 and thepiezoelectric film 6 can be formed by using a vapor phase method such asa laser ablation method, a sputter method or the like.

Then, as shown in FIG. 3( e), an upper electrode 7 formed of Pt isformed on the piezoelectric film 6, whereby the piezoelectric element 1is obtained. The upper electrode 7 can be formed by a sputter method orthe like, like the lower electrode 7,

In the piezoelectric element 1 thus obtained, the piezoelectric film 6that is formed of a relaxor material is formed on the seed layer 5 thatis preferentially oriented to (100), such that the piezoelectric film isalso preferentially oriented excellently to pseudo cubic (100), andtherefore has a high piezoelectric constant and exhibits a greaterdeformation to an applied voltage.

EMBODIMENT EXAMPLE

The piezoelectric layer 1 was fabricated as follows based on amanufacturing method shown in FIGS. 3( a)-(e).

First, a lower electrode 4 formed of Pt with a (111) orientation wasformed over a substrate 2 through an elastic film 3 by a sputter method.

Next, a precursor solution of Pb (Zr_(0.6)Ti_(0.4))O₃(=PZT) was preparedas follows.

Metal reagents of lead acetate, zirconium butoxide and titaniumisopropoxide were prepared, respectively, and mixed in a molar ratiothat corresponds to PZT to be formed, the mixed material was dissolved(dispersed) in butyl cellosolve, and diethanolamine was further added inthe solution as a stabilizing agent for the solution, to obtain theprecursor solution.

Then, the precursor solution was coated on the lower electrode 4described above by a spin coat method (precursor solution coating step),a thermal treatment (dry treatment) was then performed at a temperaturethat was about 10° C. higher than the solvent to thereby remove thesolvent (dry thermal treatment step), a heat treatment was performed atabout 350° C. to dissolve and remove ligands of the organic metals(cleaning thermal treatment step), and then a rapid thermal anneal (RTA)was performed in an oxygen atmosphere to heat at about 600° C., therebycausing crystallization to form the seed layer 5. The film thickness ofthe seed layer was 40 nm.

Next, a precursor solution of (1−x)Pb(Mg_(1/3)Nb_(2/3)) O₃-xPbTiO₃(=PMN−PT) was prepared as follows.

Metal reagents of lead acetate, titanium isopropoxide, magnesiumacetate, and niobium ethoxide were prepared, respectively, and mixed ina molar ratio that corresponds to PMN−PT to be formed, the mixedmaterial was dissolved (dispersed) in butyl cellosolve, anddiethanolamine was further added in the solution as a stabilizing agentfor the solution, to obtain the precursor solution.

Then, the precursor solution was coated on the seed layer 5 describedabove by a spin coat method (precursor solution coating step), a thermaltreatment (dry treatment) was then performed at a temperature that wasabout 10° C. higher than the solvent to thereby remove the solvent (drythermal treatment step), a heat treatment was performed at about 350° C.to dissolve and remove ligands of the organic metals (cleaning thermaltreatment step), and then a rapid thermal anneal (RTA) was performed inan oxygen atmosphere to heat at about 600° C., thereby causingcrystallization to form the piezoelectric film 6.

Then, an upper electrode 7 formed of Pt was formed on the piezoelectricfilm 6 by a sputter method, and thus the piezoelectric element 1 wasobtained.

The piezoelectric film 6 in the piezoelectric element 1 thus obtainedwas examined by X-ray diffraction (XRD), and it was confirmed that itwas preferentially oriented to (100), and it was further confirmed thatit had a rhombohedral structure.

Moreover, the piezoelectric constant (d₃₁) of the piezoelectric film 6was measured, and it was high at 600 pC/N, and the leakage current wasless than 10⁻⁵ A/cm² at 100 kV/cm.

Further, the repetition durability of the piezoelectric element 1 wasexamined when 300 kV/cm was applied, and it was found to be equippedwith a high durability that can ensure 10⁹ repetitions.

It is noted here that the seed layer 5 may be composed of a plurality oflayers. For example, PbTiO₃ may be laminated to a thickness of 5 nm onthe Pt electrode for the purpose of improving the (100) orientation ofan uppermost surface of the seed layer 5. This is because PZT havingTi-rich composition that would readily have a tetragonal structure wouldreadily take a (001) preferential orientation. The film thickness can bemore readily controlled in laminating the PbTiO₃ when a sputter methodis used rather than a solution coating method. Then, a precursorsolution of Pb (Zr_(0.6)Ti_(0.4))O₃ is coated to a thickness of 40 nm.PZT in this composition range (Zr_(0.6)Ti_(0.4)) would likely have arhombohedral structure, and would likely be preferentially oriented topseudo cubic (100), when directly disposed on the PZT having atetragonal structure with a (001) orientation.

Piezoelectric films 6 were made by using relaxor materials shown in“Table” below, and their piezoelectric constants (d₃₁) were examined.All of them exhibited high piezoelectric characteristics with d₃₁>400pC/N.

TABLE Relaxor material Piezoelectric constant d₃₁ (pC/N)0.58Pb(Sc_(1/2)Nb_(1/2))O₃—0.42PbTiO₃ 5000.63Pb(In_(1/2)Nb_(1/2))O₃—0.37PbTiO₃ 4000.50Pb(Ga_(1/2)Nb_(1/2))O₃—0.50PbTiO₃ 4000.55Pb(Sc_(1/2)Ta_(1/2))O₃—0.45PbTiO₃ 4000.65Pb(Mg_(1/3)Nb_(2/3))O₃—0.35PbTiO₃ 6000.90Pb(Fe_(1/2)Nb_(1/2))O₃—0.10PbTiO₃ 4000.91Pb(Zn_(1/3)Nb_(2/3))O₃—0.09PbTiO₃ 6000.62Pb(Ni_(1/3)Nb_(2/3))O₃—0.38PbTiO₃ 5000.58Pb(Co_(1/2)W_(1/2))O₃—0.42PbTiO₃ 400

Further, a piezoelectric element 1 using PMN•PT as the piezoelectricfilm 6, in which a piezoelectric material other than PZT, for example,BaTiO₃ was used as the seed layer 5, also exhibited a piezoelectricconstant (d₃₁) at 600 pC/N.

Ink Jet Recording Head

Next, an ink jet recording head using a piezoelectric element shown inFIG. 1 is described. FIG. 4 is a side cross-sectional view schematicallyshowing a structure of an ink jet recording head using the piezoelectricelement shown in FIG. 1. FIG. 5 is an exploded perspective view of theink jet recording head. It is noted that FIG. 4 shows the head upsidedown with respect to a state in which it is normally used. Referencenumeral 50 in these figures denotes an ink jet recording head(hereafter, referred to as the head). The head 50 is equipped with ahead main body 57 and piezoelectric elements 54 provided thereon asshown in FIG. 4. The piezoelectric element 54 shown in FIG. 4 iscomposed of the lower electrode 4, the seed layer 5, the piezoelectricfilm 6 and the upper electrode 7 of the piezoelectric element 1 shown inFIG. 1 (see FIG. 5), and the elastic film 3 with the aforementionedcomponents formed thereon corresponds to an elastic plate 55. Also, thesubstrate 2 composes a main portion of the head main body 57 asdescribed below.

More specifically, the head 50 is equipped with a nozzle plate 51, anink chamber substrate 52, an elastic plate 55, and piezoelectricelements (vibration sources) 54 that are bonded to the elastic plate 55,which are housed in a base substrate 56. The head 50 forms an on-demandtype piezoelectric head.

The nozzle plate 51 is formed from, for example, a rolled plate ofstainless steel or the like, and includes multiple nozzles 511 formed ina row for jetting ink droplets. The pitch of the nozzles 511 may beappropriately set according to the printing resolution.

The ink chamber substrate 52 is fixedly bonded (affixed) to the nozzleplate 51. The ink chamber substrate 52 is formed from the substrate 2formed of Si described above, and has a plurality of cavities (inkcavities) 521, a reservoir 523 that temporarily reserves ink that issupplied from an ink cartridge 631, and supply ports 524 that supply theink from the reservoir 523 to the respective cavities 521, which aredefined by the nozzle plate 51, side walls (partition walls) 522 and theelastic plate 55 to be described below.

Each of the cavities 521 is disposed for each of the correspondingnozzles 511 as shown in FIG. 4, has a volume that is variable byvibrations of the elastic plate 55 to be described below, and is formedto eject ink by the volume change.

As a base material for obtaining the ink chamber substrate 52, in otherwords, as the substrate 2 described above, for example, a siliconsingle-crystal substrate (Si substrate) with a (110) orientation isused. Because the silicon single-crystal substrate with a (110)orientation is suitable for anisotropic etching, the ink chambersubstrate 52 can be readily and securely formed. It is noted that thissilicon single-crystal substrate is used with its surface where theelastic film 3 is formed, in other words, its surface where the elasticplate 55 is formed, being a (100) surface.

The average thickness of the ink chamber substrate 52 is notparticularly limited, but may preferably be about 10-1000 μm, and morepreferably, about 100-500 μm. Also, the volume of the ink chamber 521 isnot particularly limited, but may preferably be about 0.1-100 nL, andmore preferably, 0.1-10 nL.

The elastic plate 55 is disposed on the ink chamber substrate 52 on theopposite side of the nozzle plate 51, and a plurality of piezoelectricelements 54 are provided on the elastic plate 55 on the opposite side ofthe ink chamber substrate 52. The elastic plate 55 is formed with theelastic film 3 of the piezoelectric element 1 shown in FIG. 1 describedabove. A communication hole 531 that penetrates the elastic plate 55 inits thickness direction is formed in the elastic plate 55 at apredetermined position. Ink can be supplied from an ink cartridge 631 tobe described below to the reservoir 523 through the communication hole531.

Each of the piezoelectric elements 54 is structured with thepiezoelectric film 6 interposed between the lower electrode 4 and theupper electrode 7, as described above, and disposed in a positioncorresponding generally to a center portion of each of the cavities 521.Each of the piezoelectric elements 54 is electrically connected to apiezoelectric element driving circuit to be described below, and isstructured to operate (vibrate, deform) based on signals of thepiezoelectric element driving circuit. In other words, each of thepiezoelectric elements 54 functions as a vibration source (headactuator). The elastic plate 55 vibrates (deforms) by vibrations(deformation) of the piezoelectric element 54, and functions toinstantaneously increase the inner pressure of the cavity 521.

The base substrate 56 is formed of, for example, any one of variousresin materials, any one of metal materials, or the like, and the inkchamber substrate 52 is affixed to and supported by the base substrate56, as shown in FIG. 4.

In the head 50 having such a structure as described above, in a state inwhich a predetermined jetting signal is not inputted through thepiezoelectric element driving circuit, in other words, in a state inwhich no voltage is applied across the lower electrode 4 and the upperelectrode 6 of the piezoelectric element 54, no deformation occurs inthe piezoelectric film 6, as shown in FIG. 6( a). For this reason, nodeformation occurs in the elastic plate 55, and no volume change occursin the cavity 521. Accordingly, no ink droplet is discharged from thenozzle 511.

On the other hand, in a state in which a predetermined jetting signal isinputted through the piezoelectric element driving circuit, in otherwords, in a state in which a predetermined voltage (for example, about30V) is applied across the lower electrode 4 and the upper electrode 6of the piezoelectric element 54, a deflection deformation occurs in thepiezoelectric film 6 in its minor axis direction, as shown in FIG. 6(b). By this, the elastic plate 53 flexes by, for example, about 500 nm,thereby causing a change in the volume of the cavity 521. At thismoment, the pressure within the cavity 521 instantaneously increases,and an ink droplet is discharged from the nozzle 511.

In other words, when the voltage is impressed, the crystal lattice ofthe piezoelectric film 6 is extended in a direction perpendicular to itssurface, but at the same time compressed in a direction parallel withthe surface.

In this condition, a tensile stress works in-plane in the piezoelectricfilm 6. Therefore, this stress bends and flexes the elastic plate 55.The larger the amount of displacement (in an absolute value) of thepiezoelectric film 6 in the direction of the minor axis of the cavity521, the more the amount of flex of the elastic plate 55 becomes, andthe more effectively an ink droplet can be discharged. In the presentinvention, the piezoelectric constant (d₃₁) of the piezoelectric film 6of the piezoelectric element 54 (1) is high, as described above, and agreater deformation is generated to an impressed voltage, such that theamount of deflection of the elastic plate 55 can be large, and the inkdroplet can be discharged more efficiently.

It is noted here that the term “efficiently” implies that an ink dropletin the same amount can be jetted by a smaller voltage. In other words,the driving circuit can be simplified, and at the same time, the powerconsumption can be reduced, such that the nozzles 511 can be formed at apitch with a higher density. Alternatively, the length of the major axisof the cavity 521 can be shortened, such that the entire head can beminiaturized.

When one ejection of the ink is completed, the piezoelectric elementdriving circuit stops application of the voltage across the lowerelectrode 4 and the upper electrode 7. By this, the piezoelectricelement 54 returns to its original shape, such that the volume of thecavity 521 increases. It is noted that, at this moment, a pressure(pressure in a positive direction) works on the ink in a direction fromthe ink cartridge 631 to be described below toward the nozzle 511. Forthis reason, air is prevented from entering the ink chamber 521 from thenozzle 511, and an amount of ink matching with the jetting amount of inkis supplied from the ink cartridge 631 through the reservoir 523 to thecavity 521.

In this manner, by inputting jetting signals successively through thepiezoelectric element driving circuit to the piezoelectric elements 54at positions where ink droplets are to be jetted, arbitrary (desired)characters and figures can be printed.

To manufacture the head 50 having such a structure, first, a basematerial that becomes an ink chamber substrate 52, in other words, asubstrate 2 formed of a silicon single-crystal substrate (Si substrate)with a (110) orientation described above, is prepared. Then, an elasticfilm 3 is formed on the substrate 2 as shown in FIG. 3, and further, alower electrode 4, a seed layer 5, a piezoelectric film 6, and an upperelectrode 7 are successively formed thereon. It is noted that theelastic film 3 formed here becomes the elastic plate 55, as describedabove.

Next, the upper electrode 7, the piezoelectric film 6, the seed layer 5,and the lower electrode 4 are patterned in a manner to correspond toindividual cavities 521 to be formed, thereby forming piezoelectricelements 54 in the number corresponding to the number of the cavities521, as shown in FIG. 4.

Next, the base material (substrate 2) that becomes an ink chamber plate52 is processed (patterned), thereby forming concave sections thatbecome the cavities 521 at positions corresponding to the piezoelectricelements 54, and concave sections that become a reservoir 523 and supplyports 524 at predetermined positions.

More specifically, a mask layer that matches with the positions of theink cavities 521, the reservoir 523 and the supply ports 524 is formed,and then, a dry etching, such as, for example, a parallel flat platereactive ion etching method, inductive coupled plasma method, electroncyclotron resonance method, helicon wave excitation method, magnetronmethod, plasma etching method, ion beam etching method, or the like, ora wet etching with a highly concentrated alkaline solution in an amountof about 5 to 40 wt % of potassium hydroxide, tetramethylammoniumhydroxide or the like, is conducted.

Here, in particular, when a silicon substrate with a (110) orientationis used as the base material (substrate 2), a wet etching (anisotropicetching) using the highly concentrated alkaline solution described aboveis preferably used. In this case, in the wet etching with the highlyconcentrated alkaline solution, the elastic film 3 can function as anetching stopper, and therefore the ink chamber plate 52 can be morereadily formed.

In this manner, the base material (substrate 2) is removed by etching inits thickness direction to the extent that the elastic plate 55 (bufferlayer 3) is exposed, thereby forming the ink chamber substrate 52. It isnoted that, in this instance, portions that remain without being etchedbecome side walls 522, and the elastic film 3 exposed assumes a statethat can function as an elastic plate 55.

Next, a nozzle plate 51 formed with a plurality of nozzles 511 is bondedsuch that each of the nozzles 511 is alighted to correspond to each ofthe concave sections that become the respective cavities 521. By this,the plurality of cavities 521, the reservoir 523 and the plurality ofsupply ports 524 are defined. For bonding of the nozzle plate 51, forexample, a bonding method using adhesive, a fusing method, or the likecan be used.

Next, the ink chamber substrate 52 is attached to the base substrate 56,whereby the ink jet recording head 50 can be obtained.

In the inkjet recording head 50 thus obtained, an efficient discharge ispossible because the piezoelectric elements 54 have excellentpiezoelectric characteristics, such that the nozzles 511 can be arrangedin a higher density, a high density printing and a high-speed printingare enabled, and a further miniaturization of the entire head can beachieved.

Ink Jet Printer

An ink jet printer equipped with the aforementioned ink jet recordinghead is described. It is noted that the ink jet printer in the presentinvention includes those for printing on paper or the like, as well asdroplet discharge devices for industrial use.

FIG. 7 is a view schematically showing a structure of an embodiment inwhich an ink jet printer of the present invention is applied to anordinary printer for printing on paper or the like, wherein referencenumeral 600 in FIG. 7 is an ink jet printer. It is noted that, an upperside in FIG. 7 refers to an “upper section” and a lower side thereinrefers to a “lower section” in the following descriptions.

The ink jet printer 600 is equipped with an apparatus main body 620, inwhich a tray 621 for holding recording paper P in an upper rear sectionthereof, a discharge port 622 for discharging the recording paper P to alower front section thereof, and an operation panel 670 on an uppersurface thereof are provided.

The operation panel 670 is formed from, for example, a liquid crystaldisplay, an organic EL display or an LED lamp, and is equipped with adisplay section (not shown) for displaying error messages and the like,and an operation section (not shown) composed of various switches andthe like.

Also, the apparatus main body 620 is provided on its inside mainly witha printing device 640 having a head unit 630 that can reciprocate, apaper feeding device 650 for feeding recording paper P one by one intothe printing device 640, and a control section 660 for controlling theprinting device 640 and the paper feeding device 650.

By the control of the control section 660, the paper feeding device 650intermittently feeds the recording paper P one by one. The recordingpaper P intermittently fed passes near a lower section of the head unit630. In this moment, the head unit 630 reciprocally moves in a directiongenerally perpendicular to a feeding direction of the recording paper P,and prints on the recording paper P. In other words, the reciprocalmovements of the head unit 630 and the intermittent feeding of therecording paper P define a main scanning and an auxiliary scanning,respectively, thereby performing printing by an ink jet method.

The printing device 640 is equipped with the head unit 630, a carriagemotor 641 that is a driving source for the head unit 630, and areciprocating mechanism 642 that receives rotations of the carriagemotor 641 to reciprocate the head unit 630.

The head unit 630 includes the ink jet recording head 50 equipped withmultiple nozzles 511 in its lower section, ink cartridges 631 thatsupply inks to the ink jet recording head 50, and a carriage 632 onwhich the ink jet recording head 50 and the ink cartridges 631 aremounted.

It is noted that the ink cartridges 631 that are filled with four colorsof yellow, cyan, magenta and black may be used, to enable full-colorprinting. In this case, the head unit 630 may be provided with the inkjet recording heads 50 corresponding to the respective colors.

The reciprocating mechanism 642 includes a carriage guide shaft 643having both ends thereof supported by a frame (not shown), and a timingbelt 644 that extends in parallel with the carriage guide shaft 643.

The carriage 632 is freely reciprocally supported by the carriage guideshaft 643, and affixed to a portion of the timing belt 644.

By operations of the carriage motor 641, the timing belt 644 is moved ina positive or reverse direction through pulleys, and the head unit 630reciprocally moves, guided by the carriage guide shaft 643. During thesereciprocal movements, the ink is jetted from the ink jet recording head50, to print on the recording paper P.

The paper feeding device 650 includes a paper feeding motor 651 as itsdriving source and a paper feeding roller 652 that is rotated byoperations of the paper feeding motor 651.

The paper feeding roller 652 is composed of a follower roller 652 a anda driving roller 652 b that are disposed up and down and opposite eachother with a feeding path of the recording paper P (i.e., the recordingpaper P) being interposed between them, and the driving roller 652 b iscoupled to the paper feeding motor 651. With such a structure, the paperfeeding roller 652 can feed the multiple recording papers P disposed inthe tray 621 one by one, toward the printing device 640. It is notedthat, instead of the tray 621, a paper feeding cassette for storingrecording paper P may be mounted in a freely detachable manner.

The control section 660 is provided for printing by controlling theprinting device 640, the paper feeding device 650 and the like, based onprint data inputted from a personal computer, a host computer of adigital camera, and the like.

The control section 660 is equipped mainly with a memory that storescontrol programs and the like to control the respective sections, apiezoelectric element driving circuit that drives the piezoelectricelements (vibration source) 54 and controls ink jetting timings, adriving circuit that drives the printing device 640 (carriage motor641), a driving circuit that drives the paper feeding device 650 (paperfeeding motor 651), a communication circuit that obtains printing datafrom a host computer, and a CPU that is electrically connected to thesecircuits, and performs various controls at each of the sections,although none of them are illustrated.

Also, the CPU is electrically connected to various kinds of sensors thatcan detect the amount of ink remaining in the ink cartridges 631, andprinting environments such as the position, temperature, humidity andthe like of the head unit 630.

The control section 660 obtains printing data through the communicationcircuit, and stores the same in the memory. The CPU processes theprinting data, and outputs driving signals to the corresponding drivingcircuits based on the processed data and input data from the variety ofsensors. Based on the driving signals, the piezoelectric elements 54,the printing device 640 and the paper feeding device 650 are operated,respectively. By this, desired printing is performed on the recordingpaper P.

Because the ink jet printer 600 described above is equipped with the inkjet recording head 50 of a high performance which is capable ofarranging nozzles at a higher density, as described above, a highdensity printing and a high-speed printing become possible.

It is noted that the ink jet printer 600 in accordance with the presentinvention can also be used as a droplet discharge device that is usedfor industrial purposes, as described above. In this case, as ink(liquid material) to be jetted, a variety of functional materials may beused with their viscosity being adjusted by solvent, dispersion mediumor the like.

Furthermore, the piezoelectric element in accordance with the presentinvention is not only applied to the ink jet recording head 50 and theink jet printer 600 described above, but also applied to a variety ofother devices.

As such devices, a surface acoustic wave element, a frequency filter, anoscillator, an electronic circuit, a thin film piezoelectric resonator,and an electronic apparatus, in accordance with embodiments of thepresent invention, are described below with reference to the drawings.

Surface Acoustic Wave Element

FIG. 8 shows a surface acoustic wave element equipped with apiezoelectric element of the present invention, more specifically, apiezoelectric element having a seed layer 5 and a piezoelectric film 6shown in FIG. 1 in accordance with an embodiment of the presentinvention.

The surface acoustic wave element includes a single-crystal siliconsubstrate 11, an oxide thin film layer 12, a seed layer 13, apiezoelectric film 14, and a protection layer 15 as a protection filmformed of oxide or nitride, and an electrode 16. The electrode 16 is aninter-digital type electrode (Inter-Digital Transducer: hereafter,referred to as “IDT electrode”), and has a configuration, as viewed fromabove, of an inter-digital transducer 141, 142, 151, 152 or 153, asshown in FIG. 9 and FIG. 10.

To manufacture a surface acoustic wave element having such a structure,first, a (100) single-crystal silicon substrate is prepared as asingle-crystal silicon substrate 11.

Next, a thin film of IrO₂, TiO₂ or the like is formed, for example, byusing a laser ablation method on the single-crystal silicon substrate11, to thereby form an oxide thin film layer 12.

Next, a seed layer 5 is formed by a liquid phase method on the oxidethin film layer 12, like in the case of forming the piezoelectricelement 1, and a piezoelectric film 14 is further formed thereon by aliquid phase method.

Next, a SiO₂ film is formed by, for example, a laser ablation method onthe piezoelectric film 14 as a protection film 15. The protection film15 protects the piezoelectric film 14 from the atmosphere, and preventsinfluences by, for example, moisture and impurities in the atmosphere,and at the same time, plays a role to control temperaturecharacteristics of the piezoelectric film 14. The material of theprotection film is not limited to SiO₂ as long as such purposes arefulfilled.

Then, an aluminum thin film, for example, is formed on the protectivelayer 15, and then is patterned, thereby forming an electrode 16 havinga desired configuration, which is called IDT, to obtain the surfaceacoustic wave element shown in FIG. 8.

Because the piezoelectric film 14, which is provided in the surfaceacoustic wave element thus obtained, has excellent piezoelectriccharacteristic, the surface acoustic wave element itself has a highperformance.

Frequency Filter

FIG. 9 shows a frequency filter in accordance with an embodiment of thepresent invention.

As shown in FIG. 9, the frequency filter has a substrate 140. Thesubstrate 140 uses a substrate with which, for example, the surfaceacoustic wave element shown in FIG. 8 is formed. More specifically, thesubstrate includes, on a (100) single-crystal silicon substrate 11, anoxide thin film layer 12, a seed layer 13, a piezoelectric film 14, anda protective layer 15 formed of oxide or nitride as a protection film,laminated in this order.

On the upper surface of the substrate 140, IDT electrodes 141 and 142are formed. The IDT electrodes 141 and 142 are formed from, for example,Al or an Al alloy, and its thickness is set to about 1/100 of the pitchof the IDT electrode 141, 142. Moreover, acoustic absorber sections 143and 144 are formed on the substrate 140 in a manner to interpose the IDTelectrodes 141 and 142.

The acoustic absorber sections 143 and 144 absorb surface acoustic wavespropagating on the surface of the substrate 140. A high frequency signalsource 145 is connected with the IDT electrode 141 formed on thesubstrate 140, and a signal line is connected with the IDT electrode142.

When a high frequency signal is outputted from the high frequency signalsource 145 in the structure described above, this high frequency signalis impressed on the IDT electrode 141. As a result, surface acousticwaves are generated on the upper surface of the substrate 140. Thesurface acoustic waves propagate over the top surface of the substrate140 at a speed of approximately 5000 m/s. The surface acoustic wavespropagating from the IDT electrode 141 toward the acoustic absorbingportion 143 are absorbed at the acoustic absorbing portion 143. However,from among the surface acoustic waves propagating toward the IDTelectrode 142, only those surface acoustic waves with a specificfrequency or specific band frequency determined according to the pitchand the like of the IDT electrode 142 are converted to electric signals,and outputted to terminals 146 a and 146 b via the signal line. It isnoted that the majority of the frequency components that are not theaforementioned specific frequency or specific band frequency areabsorbed by the acoustic absorbing portion 144 after passing through theIDT electrode 142. In this way, of the electric signals supplied to theIDT electrode 141 provided in the frequency filter of the presentembodiment, only surface acoustic waves of a specific frequency orspecific band frequency can be obtained (i.e., can be filtered).

Oscillator

FIG. 4 shows an oscillator in accordance with an embodiment of thepresent invention.

As shown in FIG. 4, the oscillator has a substrate 150. As the substrate150, a substrate with the surface acoustic wave element shown in FIG. 8formed thereon, for example, is used, like the aforementioned frequencyfilter. More specifically, the substrate includes, on a (110)single-crystal silicon substrate 11, an oxide thin film layer 12, a seedlayer 13, a piezoelectric film 14, and a protection layer 15 as aprotection film formed of oxide or nitride, laminated in this order.

On the upper surface of the substrate 150, an IDT electrode 151 isformed. Furthermore, IDT electrodes 152 and 153 are formed in a mannerto interpose the IDT electrode 151. The IDT electrodes 151-153 areformed from, for example, Al or an Al alloy, and their thickness is setto about 1/100 of the pitch of each of the IDT electrodes 151-153,respectively. A high frequency signal source 154 is connected with oneof comb teeth-shape electrodes 151 a composing the IDT electrode 151,and a signal line is connected with the other comb teeth-shape electrode151 b. It is noted that this IDT electrode 151 corresponds to anelectric signal application electrode, while the IDT electrodes 152 and153 correspond to resonating electrode for resonating a specificfrequency or a specific band frequency of the surface acoustic wavesgenerated by the IDT electrode 151.

When a high frequency signal is outputted from the high frequency signalsource 154 in the structure described above, this high frequency signalis impressed on one of the IDT electrode 151, i.e., to the combteeth-shaped electrode 151 a. As a result, surface acoustic waves aregenerated on the upper surface of substrate 150 that propagate towardthe IDT electrode 152 and toward the IDT electrode 153. It is noted thatthe speed of this surface acoustic waves is approximately 5000 m/s. Ofthese surface acoustic waves, those surface acoustic waves of a specificfrequency component are reflected at the IDT electrodes 152 and 153, anda standing wave is generated between the IDT electrode 152 and the IDTelectrode 153. The surface acoustic wave of this specific frequencycomponent is repeatedly reflected at the IDT electrodes 152 and 153. Asa result, specific frequency components or specific band frequencycomponents are resonated and their amplitude increases. A portion of thesurface acoustic waves of the specific frequency component or thespecific band frequency component is extracted from the other of the IDTelectrode 151, i.e., the comb teeth-shaped electrode 151 b, and theelectric signal of the frequency (or the frequency of a certain band)corresponding to the resonance frequency between the IDT electrode 152and the IDT electrode 153 can be extracted at terminals 155 a and 155 b.

FIG. 11 are views showing an example in which the oscillator (surfaceacoustic wave element) in accordance with the present invention isemployed as a VCSO (Voltage Controlled SAW Oscillator), wherein FIG. 11(a) is a transparent view seen from the side, and FIG. 11( b) is atransparent view seen from above.

The VCSO is housed inside a metallic (aluminum or stainless steel) box60. On a substrate 61 is mounted an IC (integrated circuit) 62 and anoscillator 63. The IC 62 is an oscillation circuit that controls thefrequency impressed on the oscillator 63 in response to a voltageinputted from an external circuit (not shown).

The oscillator 63 includes IDT electrodes 65 a-65 c formed on top of asubstrate 64. This structure is roughly equivalent to the oscillatorshown in FIG. 10. It is noted that this substrate 64 includes, on a(100) single-crystal silicon substrate 11, an oxide thin film layer 12,a seed layer 13, a piezoelectric film 14, and a protective layer 15formed of oxide or nitride as a protection film, laminated in thisorder, like the aforementioned example shown in FIG. 8.

A wiring 66 is patterned onto the substrate 61 in order to electricallyconnect the IC 62 and the oscillator 63. The IC 62 and the wiring 66are, for example, connected by a wire 67 which is a metal wire or thelike, and the oscillator 63 and the wiring 66 are connected by a wire 68which is a metal wire or the like, whereby the IC 62 and the oscillator63 are electrically connected via the wiring 66.

It is noted that, the VCSO can be formed by integrally forming the IC 62and the oscillator (surface acoustic wave element) 63 onto the same Sisubstrate.

FIG. 12 shows a view schematically showing a VCSO in which the IC 62 andthe oscillator 63 are integrated. It is noted that the oscillator 63 inFIG. 10 has a structure in which the formation of the second oxide thinfilm layer 13 is omitted from the surface acoustic wave element shown inFIG. 8.

As shown in FIG. 12, the VCSO is formed in a manner that the IC 62 andthe oscillator 63 share a single-crystal silicon substrate 61 (11). TheIC 62 and electrodes 65 a (16) provided on the oscillator 63 areelectrically connected (although not shown). In the present embodiment,TFTs (thin film transistors) are especially adopted as transistors thatcompose the IC 62.

By using TFTs as transistors that compose the IC 62, in the presentembodiment, first, an oscillator 63 (surface acoustic wave element) isformed on a single-crystal silicon substrate 61. Then, TFTs that areformed on a second substrate different from the single-crystal siliconsubstrate 61 are transferred onto the single-crystal silicon substrate61, to thereby integrate the TFTs and the oscillator 63. Even if amaterial is difficult to directly form or unsuitable to form TFTs on thesubstrate, they can be excellently formed by transfer. Various methodsmay be used as the transfer method, but in particular, the transfermethod described in Japanese Laid-open Patent Application HEI 11-26733can be preferentially used.

The VCSO shown in FIG. 11 and FIG. 12 can be employed as a VCO (VoltageControlled Oscillator) for a PLL circuit shown in FIG. 13, for example.The PLL circuit is briefly explained below.

FIG. 13 is a block diagram showing the basic structure of a PLL circuit.As shown in FIG. 13, the PLL circuit includes a phase comparator 71, alow band filter 72, an amplifier 73 and a VCO 74.

The phase comparator 71 compares the phase (or frequency) of the signalinputted from an input terminal 70 and the phase (or frequency) of thesignal outputted from the VCO 74, and outputs an error voltage signal,the value of which is set according to the difference between theaforementioned signals. The low band filter 72 transmits only the lowfrequency components at the position of the error voltage signaloutputted from the phase comparator 71, and the amplifier 73 amplifiesthe signal outputted from the low band filter 72. The VCO 74 is anoscillator circuit in which the oscillation frequency is continuouslychanged within a certain range, corresponding to the voltage valueinputted.

The PLL circuit having such a structure operates so as to decrease thedifference between the phase (or frequency) inputted from the inputterminal 70 and the phase (or frequency) of the signal outputted fromthe VCO 74, and synchronizes the frequency of the signal outputted fromthe VCO 74 with the frequency of the signal inputted from the inputterminal 70. When the frequency of the signal outputted from the VCO 74is synchronized with the frequency of the signal inputted from the inputterminal 70, it matches with the signal inputted from the input terminal70 after excluding a specific phase difference, and a signal whichconforms to the changes in the input signal is outputted.

Electronic Circuit and Electronic Apparatus

FIG. 14 is a block diagram showing an electrical structure of anelectronic circuit in accordance with an embodiment of the presentinvention. It is noted that the electronic circuit in FIG. 14 is acircuit that is provided inside a cellular telephone 100 shown in FIG.15, for example. The cellular telephone 100 shown in FIG. 15 is anexample of an electronic apparatus in accordance with the presentinvention, and includes an antenna 101, a receiver 102, a transmitter103, a liquid crystal display 104, and operating buttons 105, and thelike.

The electronic circuit shown in FIG. 14 has the basic structure of anelectronic circuit provided inside the cellular telephone 100, and isequipped with a transmitter 80, a transmission signal processing circuit81, a transmission mixer 82, a transmission filter 83, a transmissionpower amplifier 84, a transceiver wave divider 85, antennas 86 a, 86 b,a low noise amplifier 87, a reception filter 88, a reception mixer 89, areception signal processing circuit 90, a receiver 91, a frequencysynthesizer 92, a control circuit 93, and an input/display circuit 94.It is noted that the cellular telephones currently in use have a morecomplicated circuit structure due to the fact that they performfrequency converting processes multiple times.

The transmitter 80 can be realized with a microphone which convertssound wave signals into electric signals, for example, and maycorrespond to the transmitter 103 in the cellular telephone 100 shown inFIG. 15. The transmission signal processing circuit 81 is a circuit forperforming such processing as D/A conversion, modulation, etc. on theelectric signal to be outputted from the transmitter 80. Thetransmission mixer 82 mixes the signal outputted from the transmissionsignal processing circuit 81 using the signal outputted from thefrequency synthesizer 92. It is noted that the frequency of the signalsupplied to the transmission mixer 82 is about 380 MHz, for example. Thetransmission filter 83 permits passage of only those signals of therequired frequency from among the intermediate frequencies (hereafterreferred to as “IF”), and cuts unnecessary frequency signals. It isnoted that the signal outputted from the transmission filter 83 isconverted to an RF signal by a converting circuit not shown in thefigures. The frequency of this RF signal is about 1.9 GHz, for example.The transmission power amplifier 84 amplifies the power of the RF signaloutputted from the transmission filter 83 and outputs this amplifiedresult to the transceiver wave divider 85.

The transceiver wave divider 85 outputs the RF signal outputted from thetransmission power amplifier 84 to the antennas 86 a and 86 b, andtransmits the signal in the form of radio waves from the antennas 86 aand 86 b. Also, the transceiver wave divider 85 divides the receptionsignal received by the antennas 86 a and 86 b, and outputs the result tothe low noise amplifier 87. It is noted that the frequency of thereception signal outputted from the transceiver wave divider 85 is, forexample, around 2.1 GHz. The low noise amplifier 87 amplifies thereception signal from the transceiver wave divider 85. It is noted thatthe signal outputted from the low noise amplifier 87 is converted to anintermediate signal (IF) by a converting circuit not shown in thefigures.

The reception filter 88 permits passage of only those signals of therequired frequency from among the intermediate frequencies (IF) thatwere converted by a converting circuit not shown in the figures, andcuts unnecessary frequency signals. The reception mixer 89 employs thesignal outputted from the frequency synthesizer 92 to mix the signalsoutputted from the transmission signal processing circuit 81. It isnoted that the intermediate frequency supplied to the reception mixer 89is, for example, around 190 MHz. The reception signal processing circuit90 performs such processing as A/D conversion, modulation, etc., to thesignal outputted from the reception mixer 89. The receiver 91 isrealized by means of a small speaker which converts electric signalsinto sound waves, for example, and corresponds to the receiver 102 inthe cellular telephone 100 shown in FIG. 17.

The frequency synthesizer 92 is a circuit for generating the signal (ata frequency of 380 MHz, for example) to be supplied to the transmissionmixer 82 and the signal (at a frequency of 190 MHz, for example) to besupplied to the reception mixer 89. The frequency synthesizer 92 isequipped with a PLL circuit for generating a signal at 760 MHz, forexample. The frequency synthesizer 92 divides the signal output fromthis PLL circuit and generates a 380 MHz frequency signal, for example,and then further divides this signal to generate a 190 MHz signal. Thecontrol circuit 93 controls the transmission signal processing circuit81, the reception signal processing circuit 90, the frequencysynthesizer 92, and the input/display circuit 94, thereby controllingthe overall operation of the cellular telephone. The input/displaycircuit 94 displays the device status to the user of the cellulartelephone 100 shown in FIG. 15, and is provided for the user to inputdirections. This input/display circuit 94 corresponds, for example, tothe liquid crystal display 104 and the operating buttons 105 on thecellular telephone 100.

In an electronic circuit of the above-described structure, the frequencyfilter shown in FIG. 9 is employed as the transmission filter 83 and thereception filter 88. The frequency that is filtered (i.e., the frequencywhich is, permitted to pass through the filter) is set separately at thetransmission filter 83 and the reception filter 88 in response to therequired frequency in the signal outputted from the transmission mixer82 and the required frequency at the reception mixer 89. The PLL circuitthat is provided within the frequency synthesizer 92 is provided withthe oscillator shown in FIG. 11 or the oscillator (VCSO) shown in FIG.12 as the VCO 74 of the PLL circuit shown in FIG. 11.

Thin Film Piezoelectric Resonator

FIG. 16 shows a thin film piezoelectric resonator in accordance with anembodiment of the present invention. Reference numeral 30 in FIG. 16denotes a thin film piezoelectric resonator of a diaphragm type,particularly used as a communication device and a communication filter.The thin film piezoelectric resonator 30 includes a resonator 33 formedthrough an elastic plate 32 over a base substrate 31 formed of asingle-crystal silicon substrate.

The base substrate 31 is formed of a single-crystal silicon substratehaving a thickness of about 200 μm with a (110) orientation, anddefines, on its bottom surface side (on the opposite side of theresonator 32), a via hole 34 penetrating from the bottom surface side toan upper surface side of the base substrate 31.

The elastic plate 32 is formed with the elastic film 3 in thepiezoelectric element 1 shown in FIG. 1 in the present embodiment, andis formed on a (110) surface of the base substrate 31. Moreover, theresonator 33 is formed with the lower electrode 4, the seed layer 5, thepiezoelectric film 6, and the upper electrode 7 in the piezoelectricelement 1 shown in FIG. 1. The thin film piezoelectric resonator 30 thuscomposed has a structure in which the main portion (except the basesubstrate 2) of the piezoelectric element 1 shown in FIG. 1 is formed asis on the base substrate 31.

It is noted that the elastic plate 32 can be formed as follows. Forexample, silicon nitride (SiN) is formed to a thickness of about 200 nmon the base substrate 31, then silicon dioxide (SiO₂) is formed thereonto a thickness of about 400 nm to 3 μm, and the elastic film 3 is formedon them, such that the laminated films of silicon nitride, silicondioxide and elastic film 3 can be used as the elastic plate 32.Alternatively, when silicon nitride and silicon dioxide films are formedon the base substrate 2, the elastic film 3 may not be formed, such thatthe elastic plate 32 can be formed with only these laminated films.

The lower electrode 4 is formed of Pt with a (111) orientation, and isthickly formed to a thickness of about 200 nm.

The seed layer 5 is formed of a perovskite type piezoelectric material,and is preferentially oriented to (100). More specifically, it is formedof PZT or the like, and is formed to a thickness of 0.1 μm or less.

The piezoelectric film 6 is formed of a relaxor material that has arhombohedral structure of a perovskite type, and preferentially orientedto pseudo cubic (100), and is formed to a thickness of about 0.9 μm.

The upper electrode 7 is formed of Pt, like the lower electrode 4.However, the upper electrode 7 is thickly formed to a thickness of about700 nm in the present embodiment.

The upper electrode 7 is provided with a wiring 37 formed of gold or thelike through a pad 36, for electrically connecting to an electrode 35formed on the elastic plate 32.

To manufacture the thin film piezoelectric resonator 30 having such astructure, first, a base material that becomes the base substrate 31, inother words, a silicon single-crystal substrate (Si substrate) with a(110) orientation described above, is prepared. Then, an elastic plate 3is formed on the Si substrate, and further, a lower electrode 4, a seedlayer 5, a piezoelectric film 6, and an upper electrode 7 aresuccessively formed thereon. When the laminated films of siliconnitride, silicon dioxide and buffer layer are used as the elastic plate32, silicon nitride and silicon dioxide are formed in this order on theSi substrate prior to forming the elastic film 3.

Then, the upper electrode 7, the piezoelectric film 6, the seed layer 5,and the lower electrode 4 are patterned so as to correspond to the viahole 34 to be formed, thereby forming the resonator 33. It is notedthat, in particular, when the lower electrode 4 is to be patterned, theelectrode 35 is also formed at the same time, separately from the lowerelectrode 4, as shown in FIG. 16.

Then, the single-crystal silicon substrate is processed (patterned) byetching or the like from its bottom side, to form the via hole 34 thatpenetrates the substrate.

Then, a pad 36 and a wiring 37 for connecting the upper electrode 7 andthe electrode 35 are formed, thereby obtaining the thin filmpiezoelectric resonator 30.

Because the piezoelectric film of the resonator has excellentpiezoelectric characteristics and therefore has a high electromechanicalcoupling factor, the thin film piezoelectric resonator 30 thus obtainedcan be used in a high-frequency area, such as, for example, a GHz band,and can excellently function despite its smallness (thinness).

FIG. 17 shows a thin film piezoelectric resonator in accordance withanother embodiment of the present invention. Reference numeral 40 inFIG. 17 denotes a thin film piezoelectric resonator. The thin filmpiezoelectric resonator 40 is different mainly from the thin filmpiezoelectric resonator 30 shown in FIG. 16 in that a via hole is notformed, but an air gap 43 is formed between the base substrate 41 andthe resonator 42.

More specifically, the thin film piezoelectric resonator 40 includes aresonator 42 formed over a base substrate 41 formed of a single-crystalsilicon substrate with a (110) orientation. The resonator 42 is formedwith a lower electrode 44, a piezoelectric material layer 45 formed of aseed layer and piezoelectric film, and an upper electrode 46, whichconsist of the same materials as those of the lower electrode 4, theseed layer 5, the piezoelectric film 6, and the upper electrode 7described above, and, in particular, the resonator 42 is formed bylaminating the lower electrode 44, the piezoelectric material layer 45and the upper electrode 46 over the air gap 43.

In the present embodiment, an elastic film 3 is formed in a state tocover the air gap 43 on the lower side of the lower electrode 44,wherein the elastic film 3 defines an elastic plate 47 like theaforementioned example.

The elastic plate 47 can also be formed as follows. Like theaforementioned example, on the base substrate 41 may be formed layers ofsilicon nitride and silicon dioxide, or only silicon dioxide may beformed, and then the elastic film 3 is formed on them, such that theselaminated layers define the elastic plate 47. Alternatively, the elasticplate 47 may be formed with laminated layers of silicon nitride andsilicon dioxide, or only silicon dioxide, without forming the elasticfilm 3.

To manufacture the thin film piezoelectric resonator 40 having such astructure, first, a film of germanium (Ge), for example, is formed byvapor deposition or the like on the base substrate 41, and is thenpatterned in the same shape as the shape of an air gap, thereby forming,a sacrificial layer.

Then, an elastic film 3 covering the sacrificial layer is formed. It isnoted that, prior to this, layers of silicon nitride and silicon dioxidemay be formed, or only a layer of silicon dioxide may be formed. Then,these buffer layers may be patterned in a desired shape.

Next, a layer covering the elastic film 3, which becomes to be a lowerelectrode 44, is formed, and then it is patterned by dry etching or thelike, thereby forming the lower electrode 44.

Then, a seed layer and a piezoelectric film covering the lower electrode44 are formed in this order, thereby forming layers with these laminatedlayers that become a piezoelectric material layer 45. Then, the layersare patterned by dry etching or the like, to form the piezoelectricmaterial layer 45.

Then, a layer covering the piezoelectric material layer 45, whichbecomes to be an upper electrode 46, is formed, and then it is patternedby dry etching or the like, thereby forming the upper electrode 46. Itis noted that, when the elastic film 3, the lower electrode 44, thepiezoelectric material layer 45 and the upper electrode 46 are formed bypatterning over the sacrificial layer in this manner, a portion of thesacrificial layer is exposed externally.

Then, the above-described sacrificial layer is etched and removed fromthe base substrate 41 by, for example, hydrogen peroxide solution(H₂O₂), thereby forming the air gap 43, whereby the thin filmpiezoelectric resonator 40 is obtained.

Because the piezoelectric film of the resonator has excellentpiezoelectric characteristics and therefore has a high electromechanicalcoupling factor, the thin film piezoelectric resonator 40 thus obtainedcan be used in a high-frequency area, such as, for example, a GHz band,and can excellently function despite its smallness (thinness).

Also, when appropriately combined with circuit composing elements suchas inductances, capacitors and the like, the above-described thin filmpiezoelectric resonator 30 or 40 composes an excellent induction filter.

The surface acoustic wave element, frequency filter, oscillator,electronic circuit, thin film piezoelectric resonator and electronicapparatus (cellular telephone 100) in accordance with the embodiments ofthe present invention were explained above. However, the presentinvention is not limited to the above-described embodiments, but rathera variety of modifications may be freely made within the scope of theinvention.

For example, the preceding embodiments were explained using a cellulartelephone as an example of an electronic apparatus and an electroniccircuit provided inside the cellular telephone as an example of anelectronic circuit. However, the present invention is not limited to acellular telephone, and may be applied to a variety of mobilecommunications devices and their internal electronic circuits.

Furthermore, the present invention is not limited to mobilecommunications devices, but may also be applied to communicationsdevices used in a stationary state such as tuners for receiving BS andCS transmissions, and their internal electronic circuits providedtherein. Moreover, the present invention is neither limited tocommunications devices employing radio waves propagating through air asthe communications carrier, but may also be applied to electronicdevices and their internal circuitry, such as HUB, which employhigh-frequency signals propagating through a co-axial cable or opticalsignals propagating through an optical cable.

1. A piezoelectric element comprising: a seed layer formed on a basesubstrate; and a piezoelectric film formed on the seed layer, whereinthe seed layer is formed of a first perovskite type material whoseorientation is oriented to pseudo cubic (100), the first perovskite typematerial being a piezoelectric material; the piezoelectric film isformed of a second perovskite type material oriented to pseudo cubic(100); and the seed layer is formed of Pb(ZrTi)O₃.
 2. A piezoelectricelement comprising: a seed layer formed on a base substrate; and apiezoelectric film formed on the seed layer, wherein the seed layer isformed of a first perovskite type material oriented to pseudo cubic(100), the first perovskite type material being a piezoelectricmaterial; the piezoelectric film is formed of a second perovskite typematerial having a rhombohedral structure oriented to pseudo cubic (100),the second perovskite type material being a relaxor material; and theseed layer is formed of Pb(ZrTi)O₃.
 3. A piezoelectric elementcomprising: a seed layer formed on a base substrate; and a piezoelectricfilm formed on the seed layer, wherein the seed layer is formed of afirst perovskite type material whose orientation is oriented to pseudocubic (100), the first perovskite type material being a piezoelectricmaterial; the piezoelectric film is formed of a second perovskite typematerial oriented to pseudo cubic (100), the second perovskite typematerial being a relaxor material; the seed layer is formed ofPb(ZrTi)O₃; and the seed layer includes a plurality of layers, and acomposition of each layer among the plurality of layers is differentfrom one another.
 4. A piezoelectric element comprising: a seed layerformed on a base substrate; and a piezoelectric film formed on the seedlayer, wherein the seed layer is formed of a first perovskite typematerial oriented to pseudo cubic (100), the first perovskite typematerial being a piezoelectric material; the piezoelectric film isformed of a second perovskite type material having a rhombohedralstructure oriented to pseudo cubic (100), the second perovskite typematerial being a relaxor material; and the seed layer includes aplurality of layers, and a composition of each layer among the pluralityof layers is different from one another.
 5. A piezoelectric elementaccording to claim 1, wherein the second perovskite type material isformed of at least one material shown by formulae as follows:(1−x)Pb(Sc_(1/2)Nb_(1/2))O₃-xPbTiO₃ (where, x is 0.10<x<0.42);(1−x)Pb(In_(1/2)Nb_(1/2))O₃-xPbTiO₃ (where, x is 0.10<x<0.37);(1−x)Pb(Ga_(1/2)Nb_(1/2))O₃-xPbTiO₃ (where, x is 0.10<x<0.50);(1−x)Pb(Sc_(1/2)Ta_(1/2))O₃-xPbTiO₃ (where, x is 0.10<x<0.45);(1−x)Pb(Mg_(1/3)Nb_(2/3))O₃-xPbTiO₃ (where, x is 0.10<x<0.35);(1−x)Pb(Fe_(1/2)Nb_(1/2))O₃-xPbTiO₃ (where, x is 0.01<x<0.10);(1−x)Pb(Zn_(1/3)Nb_(2/3))O₃-xPbTiO₃ (where, x is 0.01<x<0.09);(1−x)Pb(Ni_(1/3)Nb_(2/3))O₃-xPbTiO₃ (where, x is 0.10<x<0.38);(1−x)Pb(Co_(1/2)W_(1/2))O₃-xPbTiO₃ (where, x is 0.10<x<0.42).
 6. Apiezoelectric element according to claim 1, wherein the piezoelectricelement, in an ink jet recording head equipped with a cavity having avolume that changes, changes the volume of the cavity by a deformationof the piezoelectric film.
 7. A piezoelectric actuator equipped with thepiezoelectric element according to claim
 1. 8. An ink jet recording headequipped with a cavity having a volume that changes, comprising thepiezoelectric element according to claim 1 as a piezoelectric elementthat changes the volume of the cavity by a deformation of apiezoelectric film.
 9. An ink jet printer comprising the ink jetrecording head according to claim
 8. 10. The piezoelectric elementaccording to claim 1, the second perovskite material being formed of arelaxor material.